Investigating the role of the autophagy-lysosome pathway in epithelial cell fate during mammary gland involution

Abstract

Mammary gland involution is a two-phase process of mass cell death and tissue remodelling which occurs post-lactation to return the tissue to a pre-pregnant state. It is a process that occurs after all pregnancies and is implicated in post-partum breast cancers, which are typically highly aggressive. The first phase of mammary gland involution is driven by lysoptosis, dependent on lysosome biogenesis and induced membrane permeability. Paradoxically, autophagy is also induced during involution concomitant with changes to mitochondrial dynamics. However, involution is still not fully understood, and how the main mammary epithelial cell (MEC) lineages (basal and luminal) may differ in their responses to involution-induced death signals remains unclear.

This study aimed to explore how specific pathways may be differentially regulated in MECs during involution, with a focus on how autophagy may be implicated in cell fate outcomes. Studies in autophagy fluorescence reporter mouse models indicate that the upregulation of autophagy observed in the mammary epithelium 24 hours post-weaning is specific to luminal MECs. However, further studies are required to determine how autophagy may selectively contribute to MEC cell fate. To support in vivo investigations, I optimised a primary murine organoid model of mammary gland lactation and involution. Proteomic analysis of basal and luminal MECs in the organoid model endorsed a cell death phenotype in luminal cells, in line with the published literature. Conversely, pathways related to cell survival, growth, motility and proliferation were identified as differentially regulated in basal MECs under involution conditions. Kinomic analysis of luminal and basal MECs isolated from lactating and involuting mammary tissues and organoids supported these conclusions. Collectively, this work provides novel insights into the differential fates of MECs during involution, which is relevant to advancing our understanding of normal mammary gland biology and how this fundamental process may be linked to breast cancer risk.

Date of Award	17 Mar 2026
Original language	English
Awarding Institution	University of Bristol
Supervisor	Bethan Lloyd-Lewis (Supervisor) & Jon D Lane (Supervisor)